The fabrication of seamless tubular metal bodies from metal workpieces, for example a tubular bloom or a bloom of metal which is to be pierced and rolled, in a planetary skew rolling mill by rolling the bloom between a plurality of rolls which are usually conical, around a mandrel-like tool in the interior of the workpiece, is known.
The fabrication of seamless pipe in this manner utilizing a so-called planetary skew rolling mill is described in DE 101 07 567 (see also U.S. Pat. No. 4,501,134). A tubular bloom is supplied to such a planetary mill and is passed through a gap defined between a plurality of rolls which are rotatable about inclined axes and which roll the bloom around the mandrel-shaped internal tool.
During the rolling, significant energy is delivered to the bloom or rolled tube and the latter tends to heat up to a significant degree such that a coolant must be applied.
From DE 101 07 567 A1, therefore, it is known to effect cooling of the bloom at the region at which the bloom is deformed to a greatest extent, usually at the inlet to the gap, by spraying the cooling medium from all sides, concentrically onto the bloom. The cooling medium, generally water, is supplied at a high pressure to the gap. The cooling water removes sufficient heat so that a temperature increase of the rolled tubing is at least in part suppressed and such that an impermissible increase in temperature is prevented.
However, this technique engenders problems since, for example, the cooling medium can enter the open ends of the rolled tubing and can create difficulties in further processing. Such difficulties can arise where the liquid trapped in the tubing can form a plug or other barrier to further shaping, e.g. rolling.
When such problems can arise, the usual approach has been to try to prevent the cooling medium from entering the open end of the tubing or the bloom. This can have the disadvantage that it can reduce the rolling speed or the output of the rolling mill and even increase the reject level. Another disadvantage for avoiding the cooling at the end regions of the tubing is that the bloom or rolled tubing in these regions emerges from the mill in a hotter state than is otherwise desirable, and can easily be oxidized. The readily oxidized region of the tube must be later removed to ensure a sufficient quality of the rolled tubing.